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Question
Write the preparation of viscose rayon.
Solution
Viscose rayon is a semisynthetic fibre which is regenerated cellulose. This cellulose has been regenerated. Cellulose's molecular formula is (C6H10O5)n. A modified representation of the molecular formula of cellulose Cell-OH, is used in the reactions involved in viscose formation.
\[\ce{\underset{(cellulose pulp wood)}{Cell - OH + NaOH} -> \underset{(alkali cellulose)}{Cell -\overset{Θ}{O}\overset{⊕}{N}a +}H2O}\]
\[\begin{array}{cc}
\ce{Cell - \overset{Θ}{O}\overset{⊕}{N}a + CS2 -> Cell - O - C - \overset{Θ}{S}\overset{⊕}{N}a}\\
\phantom{...........................}||\\
\phantom{...........................}\ce{\underset{(cellulose xanthate)}{S}}
\end{array}\]
\[\begin{array}{cc}
\ce{Cell - O - C - \overset{Θ}{S}\overset{⊕}{N}a + H2O -> Cell - O - C - SH + NaOH}\\
||\phantom{...............................}||\phantom{....}\\
\ce{S}\phantom{...............................}\ce{S}\phantom{....}
\end{array}\]
\[\begin{array}{cc}
\ce{Cell - O - C - SH + H2O -> \underset{(Regenerated cellulose filaments)}{\underset{(viscose rayon)}{Cell - OH +} CS2}}
\end{array}\]
Cellulose in the form of wood pulp is treated with concentrated NaOH solution to get fluffy alkali cellulose. It is then converted to xanthate by treating with carbon disulphide. On mixing with dilute NaOH it gives viscose solution which is extruded through spinnerates of spining machine into acid bath when regenerated cellulose fibres precipitate.
